This invention relates to a diamond-coated tungsten carbide-base sintered hard alloy material for inserts of cutting tools, and more particularly to a cutting tool insert material of this kind which has greatly improved bond strength or degree of bonding of the diamond coating layer to the tungsten carbide matrix and is therefore capable of exhibiting excellent cutting performance over a long period of time.
In recent years, in development of inserts of cutting tools or the like there have been carried out many studies of the formation of diamond coating layers over surfaces of matrices formed of various materials. Conventional typical methods of forming diamond coating layers over surfaces of matrices include low pressure vapor-phase synthesization methods known as CVD Method (chemical vapor deposition method) which utilizes thermal decomposition of a gas such as CH.sub.4, PVD Method (physical vapor deposition method), etc.
However, diamond coating layers formed by these low pressure vapor-phase synthesization methods generally have low bond strength, i.e. a low degree of bonding to the matrices, and therefore it has so far been impossible to utilize sintered hard alloys having such diamond coating layers as inserts of cutting tools which are subjected to high load from the work materials.